It is known to collect selected drive performance data, such as data relating to repeatable positional errors synchronized to disk spindle rotation and to develop correctional values and apply those values within a head position servo loop of a disk drive. One such approach is described in U.S. Pat. No. 4,628,379 to Andrews, Jr., et al, and entitled "Disk Runout Compensator". The Andrews Jr., et al. approach called for averaging offsets of thirty two embedded servo sectors over eight revolutions in order to develop average values during a calibration routine executed by a microcontroller. Magnitudes of quadrature sinewaves were determined using the sum of the averages of the real vectors and the sum of the averages of the imaginary vectors for each sector location. A vector sum was then calculated in real time and applied by the microcontroller through a digital to analog converter to an analog summing junction of the head positioner servo loop. Head position information was combined with the vector sum at the analog summing junction and then passed through an analog loop compensation network before being amplified and applied as a control current to a linear head position actuator.
U.S. Pat. No. 3,881,184 to Koepcke et al., entitled "Adaptive Digital Servo System", describes a digital servo loop employing 64 embedded optical position samples per revolution. These samples resulted in digital information from which a fundamental or higher order harmonics were developed synchronous to the spindle motion. A discrete Fourier transform analysis was then applied to develop correction signals which were then applied to reduce the runout.
A further approach of the prior art has been to collect trace records of disk drives in conjunction with external logic analyzer circuitry, and then analyze the trace records to understand and characterize drive performance. These techniques have typically been employed during disk drive development or maintenance, and have not lent themselves to real-time adaptation of disk drive characteristics. While these prior approaches are representative of the prior art, they lack certain flexibility and programmability. In particular, the synchronous runout correction circuits were dedicated to that task alone, rather than being multitasked or adaptable under program control to other tasks and measurements.
Accordingly, a hitherto unsolved need has arisen for a disk drive having a fully contained on-board digital analyzer capable of taking a wide variety of programmable trace records and creating a wide variety of stimuli and responses within the head positioner servo loop without requiring external equipment or connections.